In order to meet high target bit rate requirement in an evolved UMTS Terrestrial Radio Access (E-UTRA) Network, efficient radio resource management (RRM) techniques are required. The realization of efficient RRM methods requires exchange of measurements across different network nodes. The measurement reports indicate the resource usage in a certain network node such as average transmission power level. Generally these measurements are needed before the execution of an RRM function. Since there are different types of resources, there are several kinds of measurement reports that are to be communicated between the network nodes, notably between NodeBs, in order to efficiently perform the RRM operation. Although measurement reports are critically important, excessive or unnecessary measurement reporting should be avoided in order to minimize the signaling overheads. Our key observation is that there are a multitude of radio resource measurements that need to be communicated between radio network nodes for efficient radio resource management.
In cellular systems the RRM techniques, namely admission control and handover control, play a key role in achieving the desired grade and quality of service (GoS/QoS) targets (see also the documents 3GPP TR 25.922 “Radio Resource Management Strategies” and 3GPP TS 25.331 “Radio Resource Protocol Specifications” issued by the 3rd Generation Partnership Project). The main purpose of the admission control is to ensure that the QoS of the new session can be fulfilled. Secondly, it should also ensure that the admission of a new user should not adversely affect the performance of the ongoing sessions.
In UTRA the admission control functionality is located in the radio network controller (RNC), where the radio resource control (RRC) protocol is also terminated. The admission control process in UTRA should take into account several types of resources such as downlink transmitted power, downlink channelization code usage and uplink received total wideband power (RTWP). In UTRA, similarly to admission control, the handover is also carried out by the RNC, which is aware of the resource situation of the target cells, as discussed in the document 3GPP TR 25.922 “Radio Resource Management Strategies”.
When a new call or a handover is required, it will be denied if the required resources are not available in the target cell of the target Node B.
FIG. 1 illustrates a handover attempt failure due to insufficient cell resources. That is, FIG. 1 illustrates a serving Node B sending a handover request to a target Node B. The handover request is denied by the target Node B since uplink resource blocks are either fully utilized or their usage is above a certain threshold. The handover failure can however be prevented to some extent by inquiring the resource usage at the target Node B prior to handover attempt.
FIG. 2 therefore illustrates another scenario, where the serving Node B first requests the target Node B to report its measurements, for all type of resources, in order to prevent any handover failure due to the cell resource bottleneck. Only after receiving the measurement reports does the serving Node B determine whether that possible target Node B should be the target Node B for a handover attempt. It is clear that, in this type of situation where the target Node B cannot serve a new call due to lack of resources, the complete set of measurement reporting is wasteful of bandwidth and leads to unnecessary handover latency. In case of a failure of the handover attempt, the serving Node B typically repeats the above mentioned procedures with the second best target Node B and so on.
Hence, in an existing system the situation may arise in which several handover attempts may be needed before the handover is successfully executed. Secondly this would lead to considerable signaling overheads. The above mentioned problems have been identified and realized already from the past experiences in UTRA. The current WCDMA network utilizes try/fail/adjust/reattempt way of handling resource congestions problems.
It has thus been observed to be a problem that admission control and handover control cannot be efficiently used due to an inefficient use of radio resources. It is thus an objective to reduce unnecessary measurement reports in E-UTRA and a need to specify simple mechanisms of exchanging measurement reports between the Node Bs. There is also a need for devising mechanisms whereby the congestion situation in network could be communicated between the Node Bs in simple manner. For instance, it has been proposed to multicast congestion status in the form of single level of congestion such as available free capacity. In the current proposal the congestion status does not consider the aggregation of all different types of radio, transport network and hardware resources. In addition the congestion status does not include the measured performance such as ongoing grade of service performance. However, a situation can arise in which the system is not fully congested but still the requested QoS requirements cannot be met.
According to an aspect of the present invention, a network node generates a congestion flag, indicative of measured resource usage and measured performance, and this can then be used as a basis for determining whether to attempt to access that node.
In preferred embodiments, the invention can therefore provide some of the following advantages, namely:
A simple way to indicate congestion status to the neighbour base stations and to the UEs.
Minimizing of handover failure and handover attempt failure, thereby improving grade of service. Particular advantage in distributed systems where handover is located in Node B.
Reduction of measurement reports when they are not needed. Particular advantage in distributed systems where excessive reports can overwhelm signalling links between the base stations.
Allowing the serving Node B to update the neighbour cell list. This will allow UE to do measurement on cells, which can accommodate new links. This will also reduce the number of UE measurements.
New call blocking can be reduced. Particular advantage in distributed systems where admission control is located in Node B.
Realization of multi-cell RRM in distributed architecture where there is no centralized controller with radio related information.